In recent years, carbon fibers and aramid fibers have come to be preferred over asbestos as fiber materials for use in friction materials such as automotive disk brake pads, clutch facings and so on, as they are superior in their anti-fade property over asbestos and have favorable wear properties, and one such example is proposed in Japanese patent laid open publication No. 55-104378.
However, aramid fibers are now available in a wide range of physical and chemical specifications, and these factors may affect various properties of the friction materials in regards to facility of molding, uniformity of the distributions of ingredients which may become a cause of uneven wear, and durability of the friction materials after being molded. For instance, para-aramid fibers are superior over meta-aramid fibers in heat resistance. Furthermore, since these factors affect the various properties of the friction material in such a complex manner that it is not trivial to obtain a desired friction material by varying the mixing ratio of different fiber materials. In short, since various factors related to the fiber contents of a friction material could affect its properties in highly unpredictable manner, it is extremely difficult to predict the properties of the final frictional material without carrying out extensive experiments.